The present invention relates to a time base control device, and particularly to a time base control device in an optical disk recording/reproducing apparatus in which one frame of a composite video signal (including synchronizing signals such as a horizontal synchronizing signal, a vertical synchronizing signal, and the like) is recorded on each track on an optical disk (including an opto-magnetic disk and a phase-change type optical disk) having a vertical synchronizing mark, and the recorded signal on the optical disk is reproduced or erased.
In a conventional reproducing-only video disk player, since an optical disk to be played carries a composite video signal already recorded thereon, the composite video signal is read from the optical disk and demodulated, and a phase difference of a reproducing horizontal synchronizing signal included in the demodulated composite video signal relative to a reference horizontal synchronizing signal is detected. As a result, time base control is performed in accordance with the detected phase difference. In this time base control, a spindle servo system for performing rough adjustment of the time base control is given charge of the low band of the phase difference signal, and a time base servo system constituted by a variable delay line such as a CCD or the like for performing fine adjustment of the time base control is given charge of the high band of the phase difference signal.
Since the subject signal to be detected for the spindle servo system and for the time base servo system is one and the same and is a vertical synchronizing signal (one period thereof is 63.5 .mu.sec), the low-band jitter of the spindle servo system falls within a range of about several .mu.sec and does not increase beyond the range of time base control of the time base servo system, that is, the range of variation of the variable delay line such as a CCD, even considering the eccentricity of a disk.
On the other hand, in a system in which one frame of composite video signal is recorded on each track on an optical disk and the recorded signal is reproduced or erased, no composite video signal exists on the disk before recording. As a result, spindle servo control cannot be performed by use of a reproducing horizontal synchronizing signal, unlike the above-mentioned reproducing player. Accordingly, it is possible to configure a system such that a vertical synchronizing mark VM, made of a mirror portion where no pregroove G is cut, is provided for every rotation on a disk, for example, at its inner circumference (or at its outer circumference), as shown in FIG. 1, so that the vertical synchronizing mark VM is detected in recording operation to establish vertical synchronization.
In such a system, as shown in FIG. 2, one period of phase control becomes one frame (525H) and jitter in a range of about 2.pi./5250=0.07 is required because the above-mentioned several .mu.sec corresponds to about H/10. Assuming here that, for example, phase control is to be performed on 8 bits by use of a clock having a period which is twice as long as 1H, then a phase control signal such as is shown in FIG. 3 is obtained because 256 .times.H/2 =128H. At this time, since one step is 0.5H, jitter is .+-.H/10 or less.